Add a new --exclude (-e) flag to gh pr diff that allows users to exclude
files matching glob patterns from the diff output. This is useful for
filtering out auto-generated files, vendor directories, or other noise
when reviewing pull requests.
Supports standard glob patterns and can be specified multiple times.
Patterns match against both the full path and basename.
Closes#8739
In the absence of an explicit `--color` setting, or when `--color=auto`
is passed, the pr diff command should fall back to respecting the global
colorization setting as inferred from the environment.
If the `--repo` flag is specified, then the user intends to select a
repository other than the current one. In that case, it doesn't make
sense to fall back to detecting the PR belonging to the current branch,
so throw a descriptive error instead.
